The present apparatus relates to a back pressure regulator particularly intended for use in multi-phase systems. By that, reference is made to a system which may have a mixed flow of gas in solution, water and materials which are not soluble in the water. In one particular example as many as three phases in the sample product can be mixed or the mix can be any two of the three phases. This makes back pressure regulation difficult to implement because the mixed phases each have different viscosities. For the back pressure to remain constant the valve must have a different opening for each phase dependent on the viscosity of the phases in question. It is therefore common to achieve a stable setting for one phase. In laboratory circumstances, it is very important to have available a system which can regulate the sample back pressure in a multiple phase flow. The present apparatus is such a system which particularly helps in the operation of laboratory procedures where pressure fluctuation in a dynamic circumstance may be highly undesirable. The present apparatus certainly provides that kind of regulation, overcoming fluctuations in system pressure, and also responds even to wide ranges of viscosity and/or pressure changes or pressure settings for single phase or multiple phase fluids. The present apparatus is constructed and arranged with a selected back pressure permitted in the system. Moreover, this apparatus can control flow rates which are quite small. The present apparatus also has the advantage of achieving relative high speed resetting in flow rate to assure that the back pressure is regulated. As will be understood, the speed of response can be optimized at an intermediate rate, meaning resetting is not too fast or too slow.
One of the features of the present apparatus is the use of a pressure sensor which observes the pressure in a storage system.
The storage system is pressured to and held at a desired operating level for the system being controlled. The transducer voltage for the storage is set as a reference voltage for the system. The storage system is charged with a dry inert gas, which will not become liquid at the operating pressure, preferably nitrogen. When this charging gas is placed in that portion of the equipment, the equipment is protected by gas isolation from the fluid which is actually being regulated. The fluid undergoing regulation is likely to be chemically active and can vary widely from a high measure of activity to inert condition. In any case, the fluid in question is regulated without impinging on the pressure transducer. Thus, the pressure transducer is isolated from the valving system. This is desirable because it protects a significant portion of the system from impingement with active chemicals and it provides a damping action on the rate at which pressure changes in the fluid system are transmitted to the transducer. The present apparatus is described in very general terms as an isolated pressure sensor system which is adjustable to a set level. Further, it includes a metering valve with a movable stem. Maximum control will be achieved using a long, tapered stem. The stem can be threaded so that a motor can drive the stem in both directions to advance and retract the stem, or a linear drive system can move the stem. The preferred system also includes means for installing a seat cooperative with a needle valve to control metered flow, the flow route having an inlet and vent to waste, collection or atmosphere. The needle valve and valve seat cooperative therewith provide the throttling function. In the event that a change of phase is experienced at the needle valve, this change may reflect up the system, thereby creating a pressure change. When a pressure change occurs, it is converted by the pressure transducer into a signal which is compared to the reference voltage and then is relayed to a motor, the motor being provided with a proper polarity signal, all for the purpose of driving the motor and readjusting the needle valve. The motor dynamically moves the needle valve so that setting and resettng is accomplished continuously to assure that system pressure is regulated. This also successfully operates even when a change of phase is observed at the needle valve because the needle valve has a very small volume which results in rapid reaction to signal changes.